Several welding processes are known, described for example in patents FR 2 514 280, and FR 2 163 435 or U.S. Pat. No. 3 567 900.
The first patent relates to a process for welding in a narrow gap with a preformed undulated wire, and a device for using this process. The advantage of this is that is avoids defects like a lack of fusion, the cause of these defects being the lack of mobility of the electrode tip.
This is because, considering the high ratio between the depth and width of the gap, the electrode holder cannot be inclined far enough to direct the electric arc toward the walls of the pieces to be welded. This produces areas of discontinuity or lack of material, and thereby an embrittlement of the assembly, which is harmful to good mechanical strength.
FIG. 1 is an illustration of this welding process. The electrode holder 1.1 is arranged between the two pieces to be welded 2A and 2B, and the electrode 4 deposits a weld bead 3. FIG. 1.A shows a lack of fusion defect, while FIG. 2 is a cross section of the known device described in document FR 2 514 280.
To remedy this disadvantage, one solution is given that consists of bending the electrode wire to a special preformed profile. This profile is obtained by plastic deformation. The wire comes out of the electrode holder in undulated form with a predetermined pitch and amplitude. The result is that the electrode tip oscillates as it is consumed. Whatever the application presented, this oscillation always goes alternately to one and then the other edge of the pieces to be welded, and to either side of a main centerline Yp, always parallel to the edge of one of the pieces or to the electrode holder centerline.
However, the major disadvantage of this solution is that it is not adapted to an overhead welding position.
This is because the geometry of a weld bead deposited in a gap is considered to be correct when the angle between the free surface of the bead and the edge of the piece is greater than 90.degree., as this allows a sufficient remelting of the bead by the following bead in later passes. However, in the solution presented, the combination of gravity and surface tensions in the pool of weld metal inevitably create a joint angle.times.less than 90.degree. and thus an unacceptable geometry.
FIG. 2.B gives a representation of the result sought under conditions of overhead welding where the joining angle.times.is greater than 90.degree., while FIG. 2.A is a representation of the result obtained with this first solution, with a joining angle.times.that is then unacceptable. The result in FIG. 2.B is thus physically impossible to obtain with this process, as the weld bead is not in equilibrium.
The French patent 2 163 435 is for a process and electrode wire feed device.
The solution proposed in this process, illustrated in FIG. 3, is to curve the electrode wire in such a way that the electrode tip can be oriented in the direction of one of the pieces to be welded.
This tip is thus inclined with respect to the edge of one of the welding pieces in the plane P perpendicular to the line of advance D of the electrode holder 1.3, by an angle I which must be constant.
FIG. 3.A represents the result obtained with this process in a weld from underneath.
Its advantage is thus to allow the deposit of a weld bead with a pool geometry and size that are compatible with welding in all positions. However, the disadvantage of this process is that it never completely guarantees that there will be no lack of fusion type defect because the electrode tip cannot be held mechanically in a plane P perpendicular to the advance D.
This is because the residual internal stresses in the weld wire cause this wire to turn, oscillating about the main axis Yp.
This rotation R has the direct consequence of never guaranteeing the perfect perpendicularity of the plane P, defined by the tip of the electrode e and the axis Yp with respect to the line of advance D.
FIG. 3.B illustrates this disadvantage in a view from above.
FIG. 3.C is a perspective of the various planes and axes defined above.
The tip e adopts the positions e1 and e2 in succession and randomly during the welding operation, thereby defining planes P1 and P2 that are ill adapted to the need for perpendicularity of the plane P with respect to the line of advance D.
Patent DE 3 136 526 shows a narrow-gap welding device including an external additional motor for rotating a wire guide tube in order to oscillate the electrode wire. But this device requires an inclination of the wire guide tube, for depositing an angle bead, with the disadvantage of widening the gap or the reducing its depth. Moreover, the wire guide tube is curved, which increase its wear.
The purpose of the invention is thus to allow welding in all positions, while avoiding defects of the lock of fusion type, and ensuring simplified use of the wire guide tube.